1. Field of the Invention
The present invention generally relates to an image forming apparatus using an electrophotographic recording method, such as a laser printer, a copying machine, a facsimile machine, or the like.
2. Description of the Related Art
Conventionally, image forming apparatuses using an electrophotographic method include a plurality of photosensitive drums that contribute to enhancing the speed of image forming. Various types of methods have been proposed for sequentially transferring toner images having different colors onto a recording material conveyed by an intermediate transfer belt or a conveying belt.
In such an image forming apparatus, a cartridge including a photosensitive drum or an intermediate transfer unit including an intermediate transfer belt is in a removable configuration. A driving force of a motor that is a drive unit of the main body of the image forming apparatus is transmitted to the photosensitive drum or a drive roller that is a drive member for the intermediate transfer belt or the conveying belt via a coupling unit. The coupling unit includes a first coupling provided on the side of the main body and a second coupling provided on the side of the photosensitive drum or the drive roller. The first coupling and the second coupling are configured such that a disconnected state as well as a connected state can be assumed.
When the first coupling and the second coupling are connected, the surface speed of the photosensitive drum or the belt is typically proportional to the speed of the motor. However, if the motor is started when the state of the couplings is changing from the disconnected state to the connected state, the photosensitive drum or the belt does not rotate (i.e., the surface speed is zero) even though the motor is activated. If this state continues, the surface of the photosensitive drum or the belt may be damaged, which may lead to image quality issues.
In these circumstances, Japanese Patent Application Laid-Open No. 2002-182537 discusses a method in which a low motor speed, compared to the speed that is used when an image is formed, is used until one of the couplings, which is used for transmitting a driving force generated by a motor to a photosensitive drum, is connected to the other coupling. In other words, the motor speed will be low during the connection time of the couplings. This time is based on the couplings that take the longest time in the connection.